The present invention relates to a pushing furnace for heating steel, particularly to a rolling temperature.
Pushing furnaces of the above-mentioned general type are known in the art. In a known pushing furnace, an article is heated from above and below by burners and their flue gases. The article to be heated arrests on water-cooled supporting pipes which extend parallel to the longitudinal axis of the furnace from its inlet side to its outlet side. At locations where the article arrests on the water-cooled supporting pipe, the temperature of the article is lower than at other locations, inasmuch as heating at the arresting locations of the article is obstructed and moreover heat is withdrawn to the water-cooled supporting pipe. In order to eliminate the above-mentioned temperature differential, many measures have been taken and implemented.
It is conventional to use metallic attachment members arranged on the supporting pipes so that the article to be heated rests on the attachment members which provides for insulation between the article and the water-cooled supporting pipes. In a simple case, the attachment member is formed as a relatively small prismatic rider which has both low costs and provides for relatively low effect. Improved action is provided by attachment members which are composed of a frame-like holder placed on the pipe, a plurality of pressure resistant heat insulating intermediate pieces embraced by the holder, and a metallic slider provided on the intermediate pieces. This construction is disclosed in the German Pat. No. 1,193,528. The three-part attachment members are however very expensive, particularly because the required heat resistant materials have very high prices.
German Pat. No. 1 583 379 discloses a construction in which the attachment members are arranged only in the rear part of the furnace, as considered in pushing direction of the article. In the front part of the furnace, prismatic heat-conductive sliders are arranged on the pipe. this solution provides for operational advantages. However, it possesses the disadvantage in the fact that for obtaining good temperature equalization in the article, relatively great one-piece metallic attachments (riders) extending over the greater part of the furnace length must be utilized. They have, for example, a cross-section with a height of approximately 140 millimeter and a width of approximately 100 millimeter, in order to provide for a reasonable heat insulation in this region, on the one hand, and a tolerable life time of the attachment members, on the other hand.
It is also known to subdivide the supporting pipes in two parts in the longitudinal direction of the furnace and to offset these parts relative to one another. The advantage of this construction is that the temperature differential which takes place during heating above the supporting rail can be equalized during subsequent placing on the offset supporting pipe, inasmuch as at this location unobjectionable heating from below is performed and cooling through the supporting pipe no longer takes place. It is also known to provide the offset supporting pipes with one-piece metallic attachment members (riders). In this construction excessively high lowering of the temperature in the article above the offset supporting pipe is supposed to be prevented. Because of the offset supporting pipe, a dislocation not only heating of the article by radiation of the furnace space is prevented or obstructed, but heat is also flown from the slab via the supporting face to the cooled supporting pipe. This solution is considered favorable in the sense of the temperature equalization attained and also in the sense of the required expenditures.
However, the proposed solutions are not always satisfactory in the sense of satisfying further increasing requirements to the temperature equalization and particularly to considerably increased energy costs. The one-piece metallic attachment members (riders) provide in many cases for sufficient temperature equalization above the offset supporting pipes. As was recogniced by the current inventors this however is due to the effect that the installation which surrounds the rider at its side press away during practical operation after a short service life, because the rider attached on the supporting pipe on which the insulation is provided makes small movements during the operation. Thereby, the lateral faces of the rider are heated from the furnace. This leads to relatively high temperatures of the rider and thereby to relatively small temperature differential in the article. On the other hand, this leads to the disadvantage in the fact that the hot rider withdraws very much heat to the water cooled pipe. This leads to an undesirable increase of the energy consumption.